Control apparatus for an automatic transmission of a vehicle and a control method

ABSTRACT

A control apparatus and a control method for an automatic transmission, improved over those devised to minimize torque fluctuations which, if left unchecked, give vehicle passengers a disagreeable feeling upon a gear shift. The inventive control apparatus and method, aimed at suppressing such torque fluctuations during a shift of the transmission thereby to improve robustness and provide good shift characteristics, involve recognizing an inertia phase in which the engine speed starts to drop during the shift. At the beginning of the inertia phase, hydraulic pressures supplied to frictional engaging devices in the transmission are kept constant to suppress the torque fluctuations.

FIELD OF THE INVENTION

[0001] The present invention relates to a control apparatus for anautomatic transmission of a vehicle and a control method for thattransmission. More particularly, the invention relates to an apparatusand a method for controlling hydraulic pressure in operating anautomatic transmission of a vehicle.

BACKGROUND OF THE INVENTION

[0002] A known control method of the kind outlined above typicallyinvolves keeping an engaging pressure of an engaging-side frictionalengaging device constant until a torque phase is approximately startedfor a shift-up operation, the engaging pressure getting thereafterincreased for the shift, as disclosed illustratively in Japanese PatentLaid-Open No. Hei 7-27217. The torque phase refers to a period in whichtorque alone is varied while the engine speed remains unchanged at thestart of a shift from second to third, as indicated by temporal changesof a Gf signal (to be defined later) in a timing chart of FIG. 2 of thisspecification. The torque phase is followed by a period called aninertia phase in which the clutch inside the transmission starts to beengaged and the engine speed drops accordingly.

[0003] There is a problem with the conventional control method such asone disclosed in Japanese Patent Laid-Open No. Hei 7-27217. As theengaging pressure of the engaging-side frictional engaging device isbeing raised at shift-up time from the beginning of a torque phase,torque fluctuations are increased in the first half of the subsequentinertia phase, which makes it impossible to acquire good shiftcharacteristics. Another problem is that during feedback control of theengaging pressure from the beginning of the torque phase, large torquefluctuations at the first half of the inertia phase tend to lowerrobustness (i.e., stability of the control system).

SUMMARY OF THE INVENTION

[0004] It is therefore an object of the present invention to provide anautomatic transmission control apparatus and method whereby torquefluctuations in the first half of an inertia phase are placed underfeed-forward control to enhance robustness in subsequent feedbackcontrol so that an improved repeatable shift characteristic is obtained.

[0005] The foregoing object may be achieved according to one aspect ofthe present invention, which provides an automatic transmission controlmethod and apparatus comprising two frictional engaging devices in anautomatic transmission connected to an engine, and pressure controlcommand generation means. One of the frictional engaging devices isengaged and the other device disengaged for a shift. The pressurecontrol command generation means controls hydraulic pressures suppliedto the two frictional engaging devices during the shift and variespressure control characteristics of the devices accordingly. Theautomatic transmission control apparatus further comprises: inertiaphase recognition means for recognizing an inertia phase during a shift;torque fluctuation suppression means for calculating pressure controlcommand values to keep to predetermined levels the hydraulic pressuressupplied to the frictional engaging devices at the beginning of theinertia phase thus recognized; and pressure control command value outputmeans for outputting to the pressure control command generation meansthe pressure control command values calculated by the torque fluctuationsuppression means.

[0006] Other objects and further features of the invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a system block diagram of an automatic transmissioncontrol apparatus practiced as an embodiment of the invention;

[0008]FIG. 2 is a timing chart of the embodiment in effect duringshift-up control;

[0009]FIG. 3 is a timing chart of the embodiment in effect duringshift-down control;

[0010]FIG. 4 is a graphic representation plotting optimum hydraulicpressure command values PLv/PLmax in effect when an oil temperature Toilis varied;

[0011]FIG. 5 is a graphic representation plotting the optimum hydraulicpressure command values PLv/PLmax in effect when a throttle valveopening θ is varied;

[0012]FIG. 6 is a block diagram outlining engagement-disengagementtiming control blocks that operate using a vehicle speed signal;

[0013]FIG. 7 is a timing chart showing engagement-disengagement timingsin effect during shift-down control;

[0014]FIG. 8 is a graphic representation of relations between a vehiclespeed and engagement-disengagement timings of frictional engagingdevices;

[0015]FIG. 9 is a hardware block diagram of a controller in theembodiment;

[0016]FIG. 10 is a flowchart of main control of the embodiment;

[0017]FIG. 11 is a flowchart of shift-up control of the embodiment;

[0018]FIG. 12 is a flowchart of shift-down control of the embodiment;and

[0019]FIG. 13 is a flowchart of shift-down control of another embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020]FIG. 1 outlines an automatic transmission control apparatuspracticed as an embodiment of the invention. In FIG. 1, an engine 1 is afour-cylinder engine equipped with an ignition device 2. The ignitiondevice 2 has four ignitors 3 corresponding to the four cylinders of theengine 1. An intake pipe 4 for taking air into the engine 1 has anelectronically controlled throttle 5, a fuel injection device 6 forinjecting fuel into the engine 1, and an air flow meter 7. The fuelinjection device 6 has four injectors 8 corresponding to the fourcylinders of the engine 1. The electronically controlled throttle 5causes an actuator 9 to drive a throttle valve 10 for air flow control.In a typical vehicle, the throttle valve 10 is connected to anaccelerator pedal (not shown) by a mechanical wire (not shown), the twocomponents being operated in an interlocked manner.

[0021] A crank shaft 11 of the engine 1 is furnished with a flywheel 12.The flywheel 12 has an engine speed sensor 13 that detects revolutionsof the crank shaft 12, i.e, an engine speed Ne. A torque converter 14coupled directly to the flywheel 12 is composed of a pump 15, a turbine16 and a stator 17. A torque converter output shaft 18, i.e., the outputshaft of the turbine 16, is coupled directly to a stepped transmission19. The torque converter output shaft 18 is equipped with a turbinespeed sensor 20 for measuring a turbine speed Nt. The transmission 19comprises a planetary gear 21 and frictional engaging devices 22 and 23.The devices 22 and 23 are engaged and disengaged so as to vary the gearratio of the gear 21 for the shift required. The devices 22 and 23 arecontrolled respectively by spool valves 26 and 27 and linear solenoids28 and 29 (pressure governors). The transmission 19 is coupled to anoutput shaft 24 and has a transmission output shaft speed sensor 25 (theso-called vehicle speed sensor) that detects revolutions of the shaft24. These components constitute an automatic transmission 30.

[0022] A controller 31 controls actuators for driving the engine 1 andautomatic transmission 30. The controller 31 receives such parameters asthrottle valve opening θ, turbine speed Nt, engine speed Ne,transmission output shaft speed No, transmission oil temperature Toil,accelerator pedal angle α, and acceleration sensor signal G for controlpurposes. In a specialized system, a torque sensor (not shown) attachedto the transmission output shaft 24 detects a transmission output shafttorque To and supplies a signal representing the detected torque to thecontroller 31. The torque signal, having a waveform similar to that ofthe acceleration sensor signal, may be used to control the frictionalengaging devices of the invention. Engine torque control means 37 in thecontroller 31 outputs control signals to the electronically controlledthrottle 5, to the fuel injection device 6 and to the ignition device 2.These control signals are also used to suppress torque fluctuationsduring the shift.

[0023] Illustratively, acceleration signal calculation means 32 in thecontroller 31 calculates longitudinal acceleration of the vehicle bydividing the difference between the transmission output shaft speed Noof the current calculation period on the one hand, and the transmissionoutput shaft speed No of the preceding calculation period on the otherhand, by a calculation period. Because the longitudinal acceleration ofthe vehicle is characteristically similar to the torque of thetransmission output shaft, the calculated longitudinal accelerationallows a torque phase and an inertia phase to be grasped upon a shift.That is, the state of a shift can be recognized. An alternative way tograsp the torque phase and inertia phase is by directly detecting thelongitudinal acceleration of the vehicle using an acceleration sensor.Another way is to sense the transmission output shaft torque by use of atorque sensor. If the inertia phase alone needs to be detected, theinput-output shaft speed ratio of the transmission (i.e., speed ratio)may be resorted to for detection. For shift-up control, accelerationsignal change state calculation means 33 stores an acceleration signalin effect upon generation of a shift command signal, i.e., in effectbefore a shift operation, and checks to see if a torque phase is reachedbased on the change state represented by the signal. If a torque phaseis found to be reached, stepped signal calculation means 34 calculates apressure control command value for rapidly lowering the hydraulicpressure supplied to the disengaging-side frictional engaging device 22.For shift-down control, the acceleration signal change state calculationmeans 33 stores an acceleration signal in effect before a shift commandsignal is generated, i.e., in effect before the throttle valve openingis increased. This acceleration signal, combined with the generatedshift command signal, is used to find the state of change from theacceleration signal in effect before the increase of the throttle valveopening. On the basis of the state of change thus acquired, a check ismade to see if the start of a shift operation (i.e., beginning of aninertia phase) is approached. If the start of a shift operation is foundto be imminent, the stepped signal calculation means 34 calculates apressure control command value for rapidly raising the hydraulicpressure fed to the engaging-side frictional engaging device 22.Pressure control command generation means 35 outputs the pressurecontrol command value thus calculated to the linear solenoid 29.

[0024] For shift-up control, the acceleration signal change statecalculation means 33 detects an inertia phase based on the changes inthe above acceleration signal, to see if the inertia phase is in itsfirst or latter half. When the inertia phase is found to be in its firsthalf, torque fluctuation suppression means 36 calculates a constantpressure control command value to keep constant, with respect to thepreceding torque phase, the hydraulic pressure supplied to theengaging-side frictional engaging device 22. For shift-down control, theacceleration signal change state calculation means 33 detects an inertiaphase based on the changes in the above acceleration signal, to see ifthe inertia phase is in its first or latter half. When the inertia phaseis found to be in its first half, the torque fluctuation suppressionmeans 36 calculates a constant pressure control command value to keepconstant, with respect to the preceding torque phase, the hydraulicpressure supplied to the disengaging-side frictional engaging device 23.Thereafter, the appropriate pressure control command value is calculatedto raise or lower the hydraulic pressure fed to the frictional engagingdevice 22 or 23 for the shift-up or shift-down operation. Alternatively,feedback hydraulic pressure control may be instituted by use of anacceleration signal.

[0025]FIG. 2 is a timing chart of the embodiment in effect duringshift-up control, illustratively for a shift from second to third. InFIG. 2, solid lines represent control characteristics of the embodiment.When a shift command signal designates a shift from second to third, anacceleration signal Gf, i.e., a longitudinal vehicle acceleration signalhaving been filtered, is stored as an acceleration signal Gs in effectbefore the shift. A change constant for the acceleration signal Gf bywhich to recognize the beginning of a torque phase is set as anacceleration Gshift. In view of ensuring the precision of torque phaserecognition, the acceleration Gshift needs to be varied depending on thechanges in the throttle valve opening θ, i.e., on the magnitude ofengine load. An engaging hydraulic pressure command signal HC is raisedsimultaneously with the setting of the change constant. The value of thesignal HC to rise is determined in advance by a matching process. Theengaging hydraulic pressure command signal Hc needs to be varied invalue depending on the changes in the transmission oil temperature Toiland throttle valve opening θ. Such variations are stored beforehand indata tables as shown in FIGS. 4 and 5. A disengaging hydraulic pressurecommand signal BB is made to fall as shown in FIG. 2. The value of thesignal BB to fall should be set beforehand to establish, when the signalis made to fall, a hydraulic pressure bordering on disengagement inorder to advance the disengagement time of the disengaging-sidefrictional engaging device. The signal BB also needs to be varied invalue depending on the changes in the transmission oil temperature Toiland throttle valve opening θ.

[0026] When the torque phase begins, the disengaging hydraulic pressurecommand signal BB is made to fall in stepped fashion to disengage thedisengaging-side frictional engaging device at a point in time marked bya small hollow circle on the plotted characteristic of the accelerationGf. The acceleration Gf in effect at this point is regarded as anacceleration Gshift. In this manner, getting the disengaging hydraulicpressure command signal BB to fall allows the actual disengaginghydraulic pressure to synchronize with a point in time marked by anotherhollow circle at the end of the torque phase. The operation provides animproved shift characteristic. For the present system, the fall time ofthe stepped signal BB is kept from exceeding 100 ms in view of hydraulicresponsiveness. Letting the signal fall time exceed 100 ms will producevibrations in the acceleration Gf in the inertia phase as indicated bybroken lines in FIG. 2. Such vibrations are attributable to a delayeddisengagement of the disengaging-side frictional engaging device.

[0027] With the inertia phase started, the engaging hydraulic pressurecommand signal HC derived from the torque phase needs to be keptconstant in value (see part A in FIG. 2) so that the acceleration Gfwill coincide with a target acceleration Gtar (i.e., target accelerationsignal). Where the longitudinal acceleration of the vehicle is notconsidered, raising the engaging hydraulic pressure command signal HC invalue illustratively from the beginning of the inertia phase boosts theacceleration Gf to a level appreciably higher than the targetacceleration Gtar. This produces torque fluctuations indicated by dashedlines in FIG. 2. In the latter half of the inertia phase, the value ofthe engaging hydraulic pressure command signal HC needs to be controlledby feedback of the acceleration Gf in order to suppress torquefluctuations.

[0028]FIG. 3 is a timing chart of the embodiment in effect duringshift-down control, illustratively for a shift from third to second. InFIG. 3, solid lines represent control characteristics of the embodiment.Before a shift command signal designates a shift from third to second,the acceleration Gf is regarded and stored as an acceleration signal Gs.A check is then made to see if the shift command signal is generated. Ifthe signal is found to be generated, a disengaging hydraulic pressurecommand signal HD is made to fall. The value of the signal HD to fall isdetermined in advance by a matching process. The disengaging hydraulicpressure command signal HD needs to be varied in value depending on thechanges in the oil temperature Toil and throttle valve opening θ. Suchvariations are stored beforehand in data tables as shown in FIGS. 4 and5. To detect the engine load more precisely requires using theacceleration signal Gs mentioned above. An engaging hydraulic pressurecommand signal BC is raised simultaneously with the generation of theacceleration command signal. The value of the command signal BC to riseshould be set beforehand to establish, when the signal is raised, ahydraulic pressure bordering on disengagement in order to advance theengagement time of the engaging-side frictional engaging device. Thesignal BC also needs to be varied in value depending on the changes inthe transmission oil temperature Toil and throttle valve opening θ.

[0029] To minimize the rate of decrease in the acceleration Gf after theinertia phase has started requires keeping the disengaging hydraulicpressure command signal HD to a constant value in the inertia phase (seepart B in FIG. 3). Where the longitudinal acceleration of the vehicle isnot considered, lowering the disengaging hydraulic pressure commandsignal HD in value illustratively from the beginning of the inertiaphase quickly reduces the acceleration Gf to a level appreciably lowerthan the target acceleration Gtar, as indicated by dashed lines in FIG.3. From the latter half of the inertia phase to the beginning of atorque phase, the value of the disengaging hydraulic pressure commandsignal HD needs to be controlled by feedback of the acceleration Gf inorder to suppress torque fluctuations.

[0030] In the latter half of the inertia phase, the engaging hydraulicpressure command signal BC is made to rise in stepped fashion to engagethe engaging-side frictional engaging device 23 at a point in timemarked by a small hollow circle on the plotted speed ratiocharacteristic. A speed ratio value k10 at the hollow circle is obtainedthrough matching in consideration of hydraulic responsiveness. Thisallows the actual engaging hydraulic pressure to synchronize with apoint in time marked by another hollow circle at the beginning of thetorque phase. The operation provides a good shift characteristic. If thestepped signal of the engaging hydraulic pressure command value BC isdelayed as indicated by broken line in FIG. 3, the engagement of thefrictional engaging device 23 fails to coincide with the start of thetorque phase. The delay in the engagement of the frictional engagingdevice 23 adversely affects the rise in acceleration in the torquephase. As a result, the driver's feel of acceleration during ashift-down worsens.

[0031]FIG. 4 graphically plots optimum hydraulic pressure command valuesPLv/PLmax in effect when the oil temperature Toil is varied. In FIG. 4,a solid and a braided line represent tendencies for shift-up andshift-down control respectively. The optimum hydraulic pressure commandvalue PLv/PLmax is defined as the rate of increase in the engaginghydraulic pressure command value HC for shift-up control, and as therate of decrease in the engaging hydraulic pressure command value HC forshift-down control. For both shift-up and shift-down control, theoptimum command value drops as the oil temperature Toil rises. It isknown that the lower the oil temperature Toil, the greater the viscosityof the oil in the transmission. Thus to supply the frictional engagingdevice with a constant hydraulic pressure requires setting a largerhydraulic pressure command value the lower the oil temperature Toil. Thecommand values for shift-up control differ from those for shift-downcontrol. This is because, with the oil temperature Toil held constant,the engaging and disengaging hydraulic pressures for the frictionalengaging devices come on their minimum hydraulic pressure side.

[0032]FIG. 5 graphically plots the optimum hydraulic pressure commandvalues PLv/PLmax in effect when the throttle valve opening θ is varied.In FIG. 5, a solid and a braided lie represent tendencies for shift-upand shift-down control respectively. The definition of the optimumhydraulic pressure command value PLv/PLmax is the same as in the case ofFIG. 4. For shift-up control, the command value tends to rise as thethrottle valve opening θ is increased. That is, when the engine load isgetting higher, the force being applied to a frictional engaging devicereaches a point where the device begins to slip. To prevent the slippagerequires correcting the hydraulic pressure command values as shown inFIG. 5. For shift-down control, when the engine load is increasedprogressively, the frictional engaging device does not slip graduallybut is immediately disengaged. In this case, a shortened shift time letsthe engine speed rise abruptly, causing a drop in the inertia torque.This is the point where, with the throttle valve opening θ increased,the hydraulic pressure command value needs to be corrected downward.

[0033]FIG. 6 outlines the engagement-disengagement timing control blocksof the embodiment operating by use of the vehicle speed signal. Thetransmission output shaft speed No input to the controller 31 isconverted to a vehicle speed signal by vehicle speed signal calculationmeans 40. Engagement-disengagement timing calculation means 41calculates pressure control command values for obtainingengagement-disengagement timings of the frictional engaging devices byuse of the relations between the vehicle speed signal and thoseengagement-disengagement timings. The pressure control command valuesthus calculated are output to the linear solenoids 28 and 29 by thepressure control command generation means 35. As shown in FIG. 8 (to beexplained later), the above relations vary with shift type. Thuspressure control command generation means 42 and shift type recognitionmeans 43 need to be used to input the recognized shift type(third-to-first shift, third-to-second shift, etc.) to the calculationmeans 41, whereby different characteristics of different shifts arecalculated. The result is obtained alternatively where the vehicle speedsignal derived from the transmission output shaft speed is replaced by atransmission input shaft speed and the speed ratio.

[0034]FIG. 7 is a timing chart showing engagement-disengagement timingsin effect during shift-down control. Illustratively, when a shiftcommand signal Ss designates a shift from third to second, it isnecessary to cause the disengaging hydraulic pressure command signal HDto fall in preparation for a disengagement and cause the engaginghydraulic pressure command signal BC to rise to prepare for anengagement. The timings for starting a rise and a fall of the signalsare determined in reference to a point in time at which the disengaginghydraulic pressure command signal HD falls. In FIG. 7, referencecharacter b indicates a case where the engaging hydraulic pressurecommand signal BC is raised earlier than the point in time for thedisengaging hydraulic pressure command signal HD (shown by solid line)to fall. Reference character c represents a case in which the engaginghydraulic pressure command signal BC is raised later than the point intime for the disengaging hydraulic pressure command signal HD to fall.Where the shift type is different, the timing for the disengaginghydraulic pressure command signal HD to fall is delayed by a period ofd. A period of a is the time required for the engaging-side frictionalengaging device to attain a hydraulic pressure bordering on engagement.

[0035]FIG. 8 graphically depicts typical relations between the vehiclespeed and engagement-disengagement timings of the frictional engagingdevices. The engagement-disengagement timings are found to be expressedin an approximately linear fashion relative to the vehicle speed on theaxis of abscissa. The plus and minus sides in FIG. 8 correspondrespectively to the periods a and b in FIG. 7. FIG. 8 showscharacteristics of a third-to-second shift and a fourth-to-second shift.The reason for the characteristics to vary with the shift type isattributed to the width of speed ratio. For example, a fourth-to-secondshift involves a greater width of speed ratio leading to larger inertiatorque fluctuations. This requires prolonging the timings for engagementand disengagement with respect to the same vehicle speed so that theshift will take longer to be accomplished.

[0036]FIG. 9 is a hardware block diagram of the controller 31. As shownin FIG. 9, the controller 31 is made up of a filter 45 along with awaveform shaping circuit 46 for receiving signals from various sensors56, of a single-chip microcomputer 47, and of a driving circuit 48 foroutputting driving control signals to actuators 57 such as valves. Themicrocomputer 47 includes a CPU (central processing unit) 49 forcarrying out various operations, a ROM (read-only memory) 50 for storingprograms and data to be executed by the CPU 49, a RAM (random accessmemory) 51 for temporarily accommodating various data, a timer 52, anSCI (serial communication interface) circuit 53, an I/O (input-output)circuit 54, and an A/D (analog-to-digital) converter 55. The functionsof the controller 31 are accomplished by the CPU 49 carrying outappropriate operations based on the programs and data held in the ROM 50and RAM 51.

[0037] The above-described single-chip hardware configuration of thecontroller 31 may be replaced alternatively with a plurality ofsingle-chip microcomputers communicating via a dual-port RAMarrangement. Another alternative is to have a plurality of single-chipmicrocomputers communicating over a LAN (local area network).

[0038]FIGS. 10, 11 and 12 are flowcharts of control for the embodimentaccording to the invention. FIG. 10 is a main control flowchart of theembodiment. In step 60 of FIG. 10, the shift command signal Ss, throttlevalve opening θ, transmission output shaft speed No, oil temperatureToil, acceleration G, and turbine speed Nt are read. In step 61, anacceleration Gf is calculated through filtering by use of a function f1of the acceleration G. In step 62, a vehicle speed Vsp for control ofthe engagement-and disengagement timings of the frictional engagingdevices for a shift-down is calculated by use of a function f2 of thetransmission output shaft speed No. In step 63, a speed ratio gr iscalculated by use of the transmission output shaft speed No and turbinespeed Nt. In step 64, the acceleration Gf is substituted for anacceleration Gd(n), i.e., a pre-shift acceleration signal used forshift-down control. In step 65, the shift command signal Ss is used tojudge the shift type (e.g., shift-up or shift-down). If a shift-up isrecognized, steps 66 and 67 are reached in which flags Flg32 and Flgmadfor shift-down control are set to 0 each. In step 68, the processing ofFIG. 11 is carried out. If a shift-down is recognized in step 65, steps69 and 70 are reached in which flags Flg23 and flgmax for shift-upcontrol are set to 0 each. In step 71, the processing of FIG. 12 iscarried out. In step 72, the engaging hydraulic pressure command signalHC, disengaging hydraulic pressure command signal BB, disengaginghydraulic pressure command signal HD and engaging hydraulic pressurecommand signal BC acquired in the processes of FIGS. 11, 12 and 13 areoutput. The example cited here is related to the second-to-third shiftand third-to-second shift shown in FIGS. 2 and 3. Finally, the currentacceleration Gd(n) is substituted for the preceding accelerationGd(n−1), and processing returns.

[0039]FIG. 11 is a shift-up control flowchart of the embodiment. Theprocessing of FIG. 11 applies when the timing chart of FIG. 2 is ineffect. In step 74 of FIG. 11, a check is made to see if the flag Flg23is set to 1, the flag Flg23 being used to keep constant the accelerationGs to be calculated in step 75. If the flag Flg23 is set to 1 in step76, step 77 is directly reached from the next time on. In step 77, anacceleration Gshift is calculated by use of a function f3 of thethrottle valve opening θ, the acceleration Gshift being used to check ifa shift-up has started, i.e., if a torque phase has begun. Theacceleration Gshift plots a curve going upward to the right as thethrottle valve opening θ is progressively increased. In step 78, a checkis made to see the flag Flgmax is set to 1, the flag Flgmax being usedto skip step 79 (Gf≦Gs−Gshift?) from the next time on if the result ofthe check in step 79 is positive (i.e., “YES”). When the flag Flgmax isset to 1 in step 80, step 81 is reached in which the disengaginghydraulic pressure command signal BB is maximized in value to disengagethe disengaging-side frictional engaging device. If the result of thecheck in step 79 is negative (i.e., “NO”), step 80 is reached. In step80, a hydraulic pressure maintenance constant k1 bordering ondisengagement is substituted for the value BB. In step 83, a check ismade to see if the speed ratio gr is equal to or less than a constantk2. The check in step 83 is intended to verify whether part A in FIG. 2has ended. If the result of the check in step 83 is negative (“NO”),step 84 is reached in which a hydraulic pressure command value k4 forsuppressing torque fluctuations at the beginning of an inertia phase issubstituted for the engaging hydraulic pressure command value HC. If theresult of the check in step 83 is positive (“YES”), step 85 is reached.In step 85, a check is made to see if the difference between a targetacceleration Gtar and the acceleration Gf is zero. If the result of thecheck in step 85 is positive (“YES”), step 86 is reached in which zerois substituted for a corrective hydraulic pressure ΔHC. If the result ofthe check in step 85 is negative (“NO”), step 87 is reached in which thedifference between the target acceleration Gtar and the acceleration Gfis multiplied by a gain k3 to calculate the corrective hydraulicpressure ΔHC. In step 88, the corrective hydraulic pressure ΔHC is addedto the constant k4 used in step 84. Processing then returns to step 68of main control.

[0040]FIG. 12 is a shift-down control flowchart of the embodiment. Theprocessing of FIG. 12 applies when the timing chart of FIG. 3 is ineffect. In step 90 of FIG. 12, a check is made to see if the flag Flg32is set to 1, the flag Flg32 being used to keep constant the accelerationGs to be calculated in step 91. If the flag Flg32 is set to 1 in step92, step 94 is directly reached from the next time on. In step 94, acheck is made to see if the flag Flgmad is set to 1, the flag Flgmadbeing used to skip step 95 from the next time on if the result of thecheck in step 95 (gr≧k10) is positive (“YES”). If the flag Flgmad is setto 1 in step 96, step 97 is reached in which the engaging hydraulicpressure command value BC is maximized in value to engage theengaging-side frictional engaging device. If the result of the check instep 95 is negative (“NO”), step 98 is reached. In step 98, a hydraulicpressure maintenance constant k5 bordering on disengagement is input tothe engaging hydraulic pressure command value BC. The value k10 used instep 95 is a speed ratio value at which the start of acceleration in thetorque phase is satisfactory, as explained with reference to FIG. 3. Instep 99, a check is made to see if the speed ratio gr is equal to orgreater than a constant k6. The check in step 99 is intended to verifywhether part B in FIG. 3 has ended. If the result of the check in step99 is negative (“NO”), step 100 is reached. In step 100, a hydraulicpressure command value k7 for suppressing torque fluctuations (i.e.,sudden drop of torque) in the inertia phase is substituted for thedisengaging hydraulic pressure command value HD. If the result of thecheck in step 99 is positive (“YES”), step 101 is reached in which acheck is made to see if the difference between the target accelerationGtar and the acceleration Gf is zero. If the result of the check in step101 is positive (“YES”), step 102 is reached in which zero issubstituted for the corrective hydraulic pressure ΔHC. If the result ofthe check in step 101 is negative (“NO”), step 103 is reached. In step103, the difference between the target acceleration Gtar and theacceleration Gf is multiplied by a gain k8 to calculate the correctivehydraulic pressure ΔHC. In step 104, the corrective hydraulic pressureΔHC is added to the constant k7 used in step 100. Processing thenreturns to step 71 of main control.

[0041]FIG. 13 is a shift-down control flowchart of another embodiment ofthe invention. In step 105 of FIG. 13, a check is made to see if thevehicle speed Vsp is equal to or higher than a vehicle speed k9 at pointzero in time shown in FIG. 8. The check in step 105 involves verifyingwhether the vehicle speed k9 is in excess of about 27 km/h. If theresult of the check in step 105 is positive (“YES”), case c in FIG. 7applies and step 106 is reached accordingly. In step 106, the constantk7 is substituted for the disengaging hydraulic pressure command valueHD. In step 107, the constant k5 is substituted for the engaginghydraulic pressure command value BC. These constants are the same asthose shown in FIG. 12. In step 108, an engagement-disengagement timetimer1 for the vehicle speed Vsp indicated in FIG. 8 is calculated byuse of a function f5 of the vehicle speed Vsp. In step 109, a check ismade to see if a flag FlgT is set to 1, the flag FlgT being used to skipstep 110 (Timer≧timer1?) from the next time on. If the flag FlgT isfound to be 1 in step 109, step 112 is reached in which a constant maxis substituted for the engaging hydraulic pressure command value BC. Ifthe result of the check in step 110 is negative (“NO”), step 99 isreached. Steps 99 through 104 are the same as those in FIG. 12. If theresult of the check in step 105 is negative (“NO”), case b in FIG. 7applies and step 113 is reached accordingly. In step 113, the constantk5 is substituted for the engaging hydraulic pressure command value BC.In step 114, a check is made to see if the time on the timer 52 shown inFIG. 9 has elapsed by the period a indicated in FIG. 7. If the result ofthe check in step 114 is negative (“NO”), step 115 is reached andprocessing returns. If the result of the check in step 114 is positive(“YES”), step 116 is reached in which the constant max is substitutedfor the command value BC to engage the frictional engaging device. Instep 117, an engagement-disengagement time timer2 for the vehicle speedVsp indicated in FIG. 8 is calculated by use of the function f5 of thevehicle speed Vsp. In step 118, a check is made to see if a flag Flgt isset to 1, the flag Flgt being used to skip step 119 (Timer≧timer2?) fromthe next time on. If the flag Flgt is found to be 1 in step 118, step121 is reached in which the constant k7 is substituted for the commandvalue HD. If the result of the check in step 119 is negative (“NO”),step 99 is reached.

[0042] As described, the present invention as embodied above suppressestorque fluctuations that can occur during a shift of the automatictransmission in which the clutch is engaged and disengaged for shiftcontrol, whereby robustness is enhanced and shift characteristics areimproved. The invention also deals effectively with torque fluctuationsincreased by oil temperature changes or over time, so that satisfactoryshift characteristics are acquired in a repeatable manner.

[0043] As many apparently different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

What is claimed is:
 1. A control apparatus for an automatic transmissioncomprising a plurality of frictional engaging devices and pressurecontrol command generation means, said plurality of frictional engagingdevice being incorporated in an automatic transmission which reduces anoutput of an engine in a vehicle, transmits the reduced engine output todriving wheels of said vehicle, and varies a speed ratio representingthe ratio of the reduction of the engine output, said plurality offrictional engaging devices being frictionally engaged and disengaged toturn on and off the transmission of the reduced engine output, at leastone of said plurality of frictional engaging devices being frictionallyengaged and at least one of the remaining frictional engaging devicesbeing disengaged to execute a shift to vary said speed ratio, saidpressure control command generation means controlling hydraulicpressures supplied to the two frictional engaging devices to effect anengagement and a disengagement of the devices at the time of said shift,said pressure control command generation means further varyingcharacteristics of hydraulic pressure control, said control apparatuscomprising: inertia phase recognition means for recognizing during saidshift a beginning of an inertia phase in which a speed of said enginevaries; and torque fluctuation suppression means for calculatingpressure control command values to keep constant the hydraulic pressuressupplied to said frictional engaging devices at the recognized beginningof said inertia phase, the calculated pressure command control valuesbeing output to said pressure control command generation means.
 2. Acontrol apparatus for an automatic transmission according to claim 1,wherein said pressure control command values calculated by said torquefluctuation suppression means are command values which keep constant thehydraulic pressures supplied to said frictional engaging devices beforecausing said hydraulic pressures to vary in accordance with a signalrepresenting said recognized beginning of said inertia phase.
 3. Acontrol apparatus for an automatic transmission according to claim 1,wherein said pressure control command values calculated by said torquefluctuation suppression means are command values which, for a shift-upwith said speed ratio varying from a large to a small value, keepconstant the hydraulic pressure supplied to an engaging-side frictionalengaging device among said plurality of frictional engaging devices,said pressure control command values being command values which, for ashift-down with said speed ratio varying from a small to a large value,keep constant the hydraulic pressure supplied to a disengaging-sidefrictional engaging device among said plurality of frictional engagingdevices.
 4. A control apparatus for an automatic transmission accordingto claim 1, wherein said torque fluctuation suppression means correctssaid pressure control command values to keep constant the hydraulicpressures supplied to said frictional engaging devices in accordancewith oil temperature changes in said automatic transmission.
 5. Acontrol apparatus for an automatic transmission according to claim 1,wherein said torque fluctuation suppression means corrects said pressurecontrol command values to keep constant the hydraulic pressures suppliedto said frictional engaging devices in accordance with load changes ofsaid engine.
 6. A control apparatus for an automatic transmissioncomprising a plurality of frictional engaging devices and pressurecontrol command generation means, said plurality of frictional engagingdevice being incorporated in an automatic transmission which reduces anoutput of an engine in a vehicle, transmits the reduced engine output todriving wheels of said vehicle, and varies a speed ratio representingthe ratio of the reduction of the engine output, said plurality offrictional engaging devices being frictionally engaged and disengaged toturn on and off the transmission of the reduced engine output, at leastone of said plurality of frictional engaging devices being frictionallyengaged and at least one of the remaining frictional engaging devicesbeing disengaged to execute a shift to vary said speed ratio, saidpressure control command generation means controlling hydraulicpressures supplied to the two frictional engaging devices to effect anengagement and a disengagement of the devices at the time of said shift,said pressure control command generation means further varyingcharacteristics of hydraulic pressure control, said control apparatuscomprising: longitudinal acceleration detection means for detecting alongitudinal acceleration of said vehicle prior to said shift;acceleration signal change state calculation means for calculating achanging value of said longitudinal acceleration prior to said shift;and stepped signal calculation means for calculating a stepped signalfor causing said pressure control command generation means to disengagethe engaged frictional engaging device in accordance with the calculatedchanging value of said longitudinal acceleration.
 7. A control apparatusfor an automatic transmission according to claim 6, wherein said steppedsignal calculated by said stepped signal calculation means is a signalchanged within 200 msec of a target value.
 8. A control apparatus for anautomatic transmission according to claim 6, wherein said stepped signalcalculated by said stepped signal calculation means is a signal fordisengaging the engaged frictional engaging device near a beginning ofan inertia phase in which the speed of said engine varies during saidshift.
 9. A control apparatus for an automatic transmission comprising aplurality of frictional engaging devices and pressure control commandgeneration means, said plurality of frictional engaging device beingincorporated in an automatic transmission which reduces an output of anengine in a vehicle, transmits the reduced engine output to drivingwheels of said vehicle, and varies a speed ratio representing the ratioof the reduction of the engine output, said plurality of frictionalengaging devices being frictionally engaged and disengaged to turn onand off the transmission of the reduced engine output, at least one ofsaid plurality of frictional engaging devices being frictionally engagedand at least one of the remaining frictional engaging devices beingdisengaged to execute a shift to vary said speed ratio, said pressurecontrol command generation means controlling hydraulic pressuressupplied to the two frictional engaging devices to effect an engagementand a disengagement of the devices at the time of said shift, saidpressure control command generation means further varyingcharacteristics of hydraulic pressure control, said control apparatuscomprising: rotating speed detection means for detecting at least one ofan output shaft rotating speed and an input shaft rotating speed of saidautomatic transmission; vehicle speed signal calculating means forcalculating a speed of said vehicle based on the rotating speed detectedby said rotating speed detection means; and clutchengagement-disengagement timing calculation means for calculatingtimings of clutch engagement and disengagement of said frictionalengaging devices on the basis of the calculated vehicle speed.
 10. Acontrol apparatus for an automatic transmission according to claim 9,wherein said clutch engagement-disengagement timing calculation meansvaries the timings of said clutch engagement and disengagement inaccordance with a type of said shift.
 11. A control method for anautomatic transmission comprising a plurality of frictional engagingdevices and pressure control command generation means, said plurality offrictional engaging device being incorporated in an automatictransmission which reduces an output of an engine in a vehicle,transmits the reduced engine output to driving wheels of said vehicle,and varies a speed ratio representing the ratio of the reduction of theengine output, said plurality of frictional engaging devices beingfrictionally engaged and disengaged to turn on and off the transmissionof the reduced engine output, at least one of said plurality offrictional engaging devices being frictionally engaged and at least oneof the remaining frictional engaging devices being disengaged to executea shift to vary said speed ratio, said pressure control commandgeneration means controlling hydraulic pressures supplied to the twofrictional engaging devices to effect an engagement and a disengagementof the devices at the time of said shift, said pressure control commandgeneration means further varying characteristics of hydraulic pressurecontrol, said control method comprising the steps of: recognizing duringsaid shift a beginning of an inertia phase in which a speed of saidengine varies; and keeping constant the hydraulic pressures supplied tosaid frictional engaging devices at the recognized beginning of saidinertia phase.
 12. A control method for an automatic transmissioncomprising a plurality of frictional engaging devices and pressurecontrol command generation means, said plurality of frictional engagingdevice being incorporated in an automatic transmission which reduces anoutput of an engine in a vehicle, transmits the reduced engine output todriving wheels of said vehicle, and varies a speed ratio representingthe ratio of the reduction of the engine output, said plurality offrictional engaging devices being frictionally engaged and disengaged toturn on and off the transmission of the reduced engine output, at leastone of said plurality of frictional engaging devices being frictionallyengaged and at least one of the remaining frictional engaging devicesbeing disengaged to execute a shift to vary said speed ratio, saidpressure control command generation means controlling hydraulicpressures supplied to the two frictional engaging devices to effect anengagement and a disengagement of the devices at the time of said shift,said pressure control command generation means further varyingcharacteristics of hydraulic pressure control said control methodcomprising the steps of: detecting a longitudinal acceleration of saidvehicle prior to said shift; calculating a changing value of saidlongitudinal acceleration prior to said shift; and calculating a steppedsignal for disengaging the engaged frictional engaging device inaccordance with the calculated changing value of said longitudinalacceleration.
 13. A control method for an automatic transmissioncomprising a plurality of frictional engaging devices and pressurecontrol command generation means, said plurality of frictional engagingdevice being incorporated in an automatic transmission which reduces anoutput of an engine in a vehicle, transmits the reduced engine output todriving wheels of said vehicle, and varies a speed ratio representingthe ratio of the reduction of the engine output, said plurality offrictional engaging devices being frictionally engaged and disengaged toturn on and off the transmission of the reduced engine output, at leastone of said plurality of frictional engaging devices being frictionallyengaged and at least one of the remaining frictional engaging devicesbeing disengaged to execute a shift to vary said speed ratio, saidpressure control command generation means controlling hydraulicpressures supplied to the two frictional engaging devices to effect anengagement and a disengagement of the devices at the time of said shift,said pressure control command generation means further varyingcharacteristics of hydraulic pressure control, said control methodcomprising the steps of: detecting at least one of an output shaftrotating speed and an input shaft rotating speed of said automatictransmission; calculating a speed of said vehicle based on the detectedrotating speed; and calculating timings of clutch engagement anddisengagement of said frictional engaging devices on the basis of thecalculated vehicle speed.